Two-piece Zirconia Oral Implants Withstand Masticatory Loads: An Investigation in the Artificial Mouth

Objective: To evaluate the fracture resistance of two-piece zirconia oral implants after long-term thermomechanical cycling in an aqueous environment. Non-loaded samples and a one-piece implant system served as control groups.

Methods: A total of 48 zirconia implants were evaluated: 16 one-piece implants (ATZ; Group A) and 32 differently connected two-piece implants (16 screwed, Group B; 16 bonded, Group C) made of Y-TZP-A (implant+abutment; B) and Y-TZP-A/ATZ (implant/abutment; C), respectively. These groups were divided into two subgroups composed of 8 samples. The samples of subgroups 1 (A1, B1, C1) were not exposed to any cyclic loading, whereas subgroups 2 (A2, B2, C2) were loaded with 10 million cycles (98 N). Subsequently, all 48 implants were statically loaded to fracture.

Results: A constant load on distinct lever arms resulted in different exerted bending moments during the dynamic loading (A2: 23.4Ncm, B2: 17.9 Ncm, C2: 32.3 Ncm). All implants survived the long-term thermomechanical cycling. For the static loading the following average bending moments were calculated: A1/A2: 362/399 Ncm; B1/B2: 398/346 Ncm; C1/C2: 380/252 Ncm. Foregoing dynamic loading significantly increased fracture resistance of Group A implants, whereas Group B/C implants showed significantly decreased values. Potentially owed to the experimental setup in an aqueous environment of 60 °C, 5/8 C2 samples showed mobility between implant and abutment due to debonding after dynamic loading conditions.

Significance: The evaluated ceramic implant systems seem to be able to resist physiological chewing forces long-term. Within the limitations of the experimental setup, the connecting mechanism of Group C implants might be a weak point.